The present invention relates to an enclosed switchboard having a vertical bus bar and unit chambers situated in front of the vertical bus bar and tiered one above the other for accommodating unit devices.
An example of enclosed switchboard of this type is shown in FIG. 1. The space inside a box-shaped frame 1 is divided by a plurality of shelf sheets 2 to form a plurality of unit chambers 3. Unit devices 9 are removably inserted in the respective unit chambers 3. Each of the unit devices 9 may comprise a circuit breaker, control relays and other control elements mounted on a common frame and electrically connected to have desired control and switching functions. Connection of the unit device 9 to vertical bus bars 5 behind an insulating cover 12 is accomplished by connectors 10 which project from the rear side of the unit device 9 (FIG. 2). When the unit device 9 is inserted in the unit chamber 3, the connectors 10 extend through openings 12a in the insulating cover 12 and are engaged with the vertical bus bars 5 (FIG. 3).
Horizontal bus bars 6 are provided in the top portion of the switchboard and are mounted to the frame 1 by tubular insulators 7 and mounting plates 8. The vertical bus bars 5 are respectively connected to the horizontal bus bars 6 and are sandwiched between an insulating cover 4 and the cover 12 for support and insulation.
The above described construction has the following disadvantages. First, to ensure that the connectors 10 are smoothly brought into engagement with the vertical bus bars 5, the edges of the vertical bus bars 5 have to be beveled. Also, a large current due to short circuit accident may cause an electromagnetic force urging the connectors 10 to open sidewardly and separate from the bus bars 5. The separation may cause arcing, and therefore welding between the connector 10 and the bus bar 5.